The brief summary of the scientific article

As I promised in previous message I provide you with a short explanation of the work we have done on the University of Warsaw using the data acquired with Universe@home project. I remind you that the article can be found at http://arxiv.org/pdf/1503.08745v1. The main subject of this article are the extreme ultra-luminous X-ray sources (EULX). Probably a bit enigmatic name, so I will start with explaining what they are.

Most stars in the Universe are the binary stars (i.e., two stars bound gravitationally). In such systems a lot of interesting phenomena occur that are prohibited for single stars.

Let's take a rare group of binary stars in which one object is the black hole (BH) and the companion is on such a close orbit that the mass is stripped from it by strong gravitational force. This material falls onto the BH but on the way it forms an accretion disk. Friction produces large temperatures which results in energetic radiation in X-ray band. We name such systems the X-ray binaries (XRB).

If we make the additional assumption that the X-ray emission is extremely energetic we will acquire the EULX systems. We are not sure what is the real nature of them. The BH may be very massive or may be similar in this case to its cousins in XRBs. Even the neutron stars (NS) are possible as accreting objects. These (and other) questions make EULX a perfect field for study.

In the presented paper we perform the numerical simulation to study the evolution of a large number of systems. In total we evolved a billion stars and from this awesome sample we dig out the rare systems whose X-ray emission is comparable to EULX. Then we performed the statistical studies and distinguished the evolutionary routes leading to the phases of this super-emission. We found that both BH and NS accretors are possible and that they should be easily differentiated by their companions.

The main outcome of this work is that EULXs are not separate group of objects among XRBs but they are a very common phase in the evolution of a large number of systems. This phase is very short (1-10,000 yr - extremely short in cosmic scale) but occurs so frequently that we are able to observe a few EULX at any time in the life of the Galaxy. Currently we observe about 500 ultra-luminous X-ray source (ULX) but only one EULX (10-1000 more luminous than ULX). The forthcoming article will deal with the regular ULXs.Grzegorz Wiktorowicz
National Astronomical Observatories,
Chinese Academy of Sciences